Magnetic recording media

Abstract

Magnetic recording media consist of a nonmagnetic substrate and at least one magnetizable layer bonded thereon and based on a magnetic material dispersed in at least one polyurethane and one polyurethaneurea (meth)acrylate, the polyurethaneurea (meth)acrylate being obtained by reacting a hydroxyl-containing poly(meth)acrylate with a mixture of di- and polyisocyanates and converting the remaining NCO groups with ammonia or primary or secondary amines into urea groups.

We claim: 
     
       1. A magnetic recording medium consisting of a nonmagnetic substrate and at least one magnetic layer formed thereon wherein said magnetic layer comprises a magnetic material dispersed in a binder mixture of a polyurethaneurea(meth)acrylate and at least one polyurethane selected from the group consisting of polyurethane elastomers and OH-containing polyureaurethanes, wherein the polyurethaneurea(meth)acrylate is obtained by reacting a poly(meth)acrylate having up to 2 terminal OH groups per mol and a weight average molecular weight of from 200 to 50,000 with a mixture of aliphatic polyisocyanates having an average functionality of from 3.0 to 6 NCO groups per mol and obtained from: from 0.1 to 10% by weight of a diisocyanate   from 20 to 80% by weight of a triisocyanate and   from 20 to 60% by weight of an isocyanate having a functionality of from 4 to 10, with the proviso that from 1.2 to 3.0 NCO groups react per OH group and the remaining NCO groups are converted with ammonia into urea groups.     
     
     
       2. A magnetic recording medium consisting of a nonmagnetic substrate and at least one magnetic layer formed thereon wherein said magnetic layer comprises a magnetic material dispersed in a binder mixture of a polyurethaneurea (meth)acrylate and at least one polyurethane selected from the group consisting of polyurethane elastomers and OH-containing polyureaurethanes, wherein the polyurethaneurea (meth)acrylate is obtained by reacting a poly(meth)acrylate having up to 2 terminal OH groups per mol and a weight average molecular weight of from 200 to 50,000 with a mixture of aliphatic polyisocyanates having an average functionality of from 3.0 to 6 NCO groups per mol and obtained from: from 0.1 to 10% by weight of a diisocyanate   from 20 to 80% by weight of a triisocyanate and   from 20to 60% by weight of an isocyanate having a functionality of from 4 to 10 with the proviso that from 1.2 to 3.0 NCO groups react per OH group and the remaining NCO groups are converted with primary or secondary amines into urea groups.     
     
     
       3. A magnetic recording medium as defined in claim 1, wherein the mixture of aliphatic polyisocyanates has an average functionality of from 3.5 to 5.0 NCO groups per mol, with the proviso that from 1.5 to 2.5 NCO groups react per OH group. 
     
     
       4. A magnetic recording medium as defined in claim 2, wherein the mixture of aliphatic polyisocyanates has an average functionality of from 3.5 to 5.0 NCO groups per mol, with the proviso that from 1.5 to 2.5 NCO groups react per OH group.